This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-289499, filed Sep. 22, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photo-excited gas processing apparatus for a semiconductor process which subjects a target substrate to a process such as CVD (Chemical Vapor Deposition) by using a process gas excited by light. The semiconductor process refers to various types of processes performed to form a semiconductor layer, insulating layer, conductive layer, and the like on a target substrate such as a semiconductor wafer or LCD substrate with a predetermined pattern, so that a semiconductor device or a structure including an interconnection, electrode, and the like to be connected to the semiconductor device is manufactured on the target substrate.
2. Description of the Related Art
In the manufacture of a semiconductor device, a target substrate, e.g., a semiconductor wafer, is subjected to various types of processes such as annealing, film formation, etching, oxidation, and diffusion. Of these processes, the specification (design rule) for the film formation technique is becoming more and more strict each year. This is because the semiconductor device is becoming higher in density and integration and the film to be formed is becoming thinner with a higher quality. Under these circumstances, photo-assisted CVD using an optical energy has been attracting attention.
When photo-assisted CVD is compared to plasma CVD, it can form a film less damaged by ions, can form a better amorphous film, and can form a film at a much lower temperature than with thermal CVD. An apparatus using photo-assisted CVD is disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication Nos. 61-183921 and 6-216041. In the apparatuses disclosed in these references, a film formation gas is activated by exciting it with ultraviolet rays or the like, thereby performing film formation.
FIG. 7 is a sectional view schematically showing a conventional photo-assisted CVD apparatus. Referring to FIG. 7, a worktable 6 incorporating a heater 4 is disposed in a process chamber 2 which can be vacuum-evacuated. A target substrate such as a semiconductor wafer W is placed on the upper surface of the worktable 6. A transmission window 8 made of, e.g., quartz, is hermetically disposed in the ceiling of the process chamber 2, and ultraviolet lamps 10 are disposed above the transmission window 8. Ultraviolet rays UV emitted from the ultraviolet lamps 10 are supplied into the process chamber 2 through the transmission window 8. In the process chamber 2, a ring pipe 12 with gas spray holes is disposed above the worktable 6 to supply a process gas (film formation gas). A ring pipe 14 with gas spray holes is disposed between the ring pipe 12 and transmission window 8 in order to supply a purge gas, e.g., an inert gas.
For example, disilane (Si2H6) is supplied into the process chamber 2 as the process gas, and is activated by being excited by the ultraviolet rays UV. A film formation material obtained by decomposing disilane forms a good-quality amorphous silicon film on the wafer surface. In this case, the film can be formed even if the wafer temperature is much lower (e.g., about 200xc2x0 C. to 300xc2x0 C.) than that for thermal CVD. Therefore, various types of thin films formed on the wafer surface in the pre-processes are least damaged thermally.
Since the film is deposited in this manner even when the process temperature is low, a film can be easily deposited also on the inner surface of the transmission window 8. For this reason, an inert gas such as Ar gas is sprayed from the ring pipe 14 to the inner surface of the window 8 to locally purge it of the process gas. This prevents an unwanted film that decreases the light transmittance from attaching to the inner surface of the transmission window 8.
The above photo-assisted CVD apparatus has the following problems. More specifically, an inert gas such as Ar gas is sprayed, as described above, in order to prevent an unwanted film from attaching to the inner surface of the transmission window 8. This spraying must be performed on the entire inner surface of the transmission window 8, and accordingly the amount of inert gas (purge gas) to be used increases very much. As the interior of the process chamber 2 is a vacuum, the flat plate-like transmission window 8 must have a very large thickness so that it has a high pressure resistance. If the transmission window 8 is thick, the quantity of light absorbed by the quartz glass increases accordingly, degrading the light utilization efficiency. A plurality of ultraviolet lamps 10 are disposed parallel to each other in a plane with respect to the transmission window 8. Hence, the arrangement of the ultraviolet lamps 10 is limited, and an arrangement with which the light intensity is further increased and an arrangement with which a better emission efficiency is provided cannot be employed.
The above problems become more and more serious as the wafer size increases from 8 inches to, e.g., 12 inches, and a solution at an early stage is sought for.
It is an object of the present invention to provide a photo-excited gas processing apparatus for a semiconductor process, in which the amount of purge gas to be used is small and the light utilization efficiency is high.
According to a first aspect of the present invention, there is provided a photo-excited gas processing apparatus for a semiconductor process, comprising:
a process chamber configured to accommodate a target substrate;
an excitation chamber connected to the process chamber through a connection path;
a process gas supply system configured to supply a process gas to the process chamber through the excitation chamber, and including a process gas port open to the excitation chamber;
an exhaust system configured to evacuate the process chamber, wherein a flow of the process gas from the process gas port to the connection path is formed in the excitation chamber by the exhaust system evacuating the process chamber;
a window consisting essentially of a light transmission material and disposed in a wall that defines the excitation chamber;
a light source disposed outside the excitation chamber to face the window, and configured to irradiate the flow of the process gas with light through the window, thereby exciting the process gas; and
a surface purge system configured to supply a purge gas along an inner surface of the window, and including a purge gas port open to the excitation chamber.
According to a second aspect of the present invention, there is provided a photo-assisted CVD apparatus for a semiconductor process, comprising:
a hermetic process chamber configured to accommodate a target substrate;
a worktable configured to support the target substrate in the process chamber;
a hermetic excitation chamber connected to the process chamber through a connection path;
a process gas supply system configured to supply a process gas to the process chamber through the excitation chamber, and including a process gas port open to the excitation chamber, the process gas being decomposed to provide a material of a film to be formed on the target substrate;
an exhaust system configured to evacuate the process chamber and set the process chamber to vacuum, wherein a flow of the process gas from the process gas port to the connection path is formed in the excitation chamber by the exhaust system evacuating the process chamber;
a window consisting essentially of a light transmission material and disposed in a wall that defines the excitation chamber;
an ultraviolet light source disposed outside the excitation chamber to face the window, and configured to irradiate the flow of the process gas with ultraviolet rays through the window, thereby exciting the process gas; and
a surface purge system configured to supply a purge gas along an inner surface of the window, and including a purge gas port open to the excitation chamber.